1. Field of the Invention
This invention relates to an oil dynamic bearing using an oil or the like as a lubrication fluid and a motor and a disk drive having the oil dynamic bearing.
2. Description of the Related Art
In recent years, the hard disk drive (HDD) has been increased in capacity and improved in quietude. The hard disk drives having a spindle motor for driving the disk supported on an oil dynamic bearing has found an increased application.
In the oil dynamic bearing, the oil held in a minuscule gap between the surface of a rotary unit and the surface of a fixed unit is caused to develop the dynamic pressure through a plurality of dynamic pressure generating grooves formed on at least one of the surfaces of the rotary unit and the fixed unit in the gap, and the rotary unit is supported rotatably by the dynamic pressure of the oil.
A motor having a dynamic bearing using an oil is known, comprising upper and lower radial bearings for supporting the radial load of the rotary unit, upper and lower thrust bearings for supporting the axial load of the rotary unit and a taper seal structure formed at the ends of the radial bearing portion and the thrust bearing portion not to scatter the oil.
This structure has the feature that an oil interface with an air is formed at the ends of each bearing portion and therefore bubbles, if generated in the oil, are easily discharged out and therefore a malfunction due to the bubbles hardly occurs.
Some examples of the malfunction due to the bubbles in the dynamic bearing include a case in which bubbles, if mixed in the minuscule gap of the dynamic bearing which should be filled up with the oil, are thermally expanded at high temperatures. As a result, the oil forcibly leaks out, the bearing surfaces facing the bubbles come into contact with each other and burn, or the uneven magnitude of the dynamic pressure of the bubbles causes instability.
The storage capacity of the HDD has so increased and the price thereof has so decreased recently that the HDD has now come to find application in various home electric appliances such as the recording equipment, the portable music player and the digital camera as well as the storage device of the personal computer.
The home electric appliances are required to be reduced in size and used in various environments. The HDD mounted in the home electric appliances, therefore, requires new characteristics not required of the personal computer. The HDD mounted on the portable devices such as the portable music player and the digital camera, for example, is required to be compact and thin, high in shock resistance and vibration resistance and have an internal power supply small in power consumption to stand the protracted use without adversely affecting the storage capacity and quietude.
In order to realize such HDD, a spindle motor for driving the disk in keeping with the characteristics described above is required, and we have studied the use of an oil dynamic bearing having an oil interface with an air at each end of the bearing as explained above.
Generally, the spindle motor carrying an oil dynamic bearing can be implemented with high-accuracy rotation, and therefore the HDD having this motor can achieve the desired storage capacity and quietude. The oil dynamic bearing having an oil interface with an air at the ends thereof, however, requires a space for holding the oil in a taper seal portion and a bearing portion, and therefore cannot be suitably reduced in size or thickness.
For this reason, the spindle motor and the HDD carrying this oil dynamic bearing is difficult to reduce in size and thickness.
The foregoing is the description of the HDD, the spindle motor and the oil dynamic bearing mounted on the HDD. A similar problem is encountered, however, also in the use of the oil dynamic bearing for motors of other applications and the devices carrying the motors.